In the use of hydraulic cements it is a conventional practice to employ accelerators which shorten the time required for the cement (or concrete) to achieve set. Suitable accelerators for use in cementitious compositions include polyvalent. metal salts of formic acid such as the alkaline earth metal or transition metal formates. Such formate salts may be used alone or in combination with other agents. For example U.S. Pat. No. 4,507,154 to Burge et al discloses a cement accelerator composed of a formic acid salt such as calcium, magnesium, iron or aluminum formate in combination with alumin hydroxide and a swellable polymer such as hydroxyethyl cellulose.
U.S. Pat. Nos. 4,191,584 (Berry) and 4,261,755 (Berry et al) disclose the use of formate accelerators in applications where rapid setting is desirable such as in cold climatic conditions or in the production of prefabricated concrete shapes. Both patents are directed to overcoming what is termed a major disadvantage, the relatively low water solubility of neutral calcium formate. Berry '584 discloses the use of calcium polyformate in an amount within the range of 0.2-5% by weight, either alone or in admixture with calcium formate. Berry et al '755 contains a similar disclosure with respect to the use of an acid formate as an accelerator.
Another application of accelerators in achieving fast setting times and high early strengths is in the formulation of cementitious compositions useful as patching or topping compositions where only limited time is available to complete the work. For example, U.S. Pat. No. 4,033,782 to Ray et al disclose a calcium aluminate cement based grouting composition in which calcium formate is used as an accelerator. The patching compositions disclosed in Ray et al contain, on a dry basis, up to about 75% aggregate (a mixture of a gravel and sand) about 20-25% high alumina cement, about 2-3% each of calcium formate and gypsum, and minor amounts of silica flour and calcium lignosulfonate.
U.S. Pat. No. 3,801,338 to Whittaker discloses an accelerator additive for use in hydraulic cements which comprises a major amount of sodium nitrate in admixture with a minor amount of calcium formate. The additive composition is disclosed as added to ordinary portland cements and to sulfate resisting cements. The additive decreases the setting time of both types of cements.
U.S. Pat. No. 3,852,081 to Lehman discloses quick-setting, high-early strength cementitious compositions based upon a portland cement component of relatively low tricalcium aluminate content. In experimental work reported in Lehman, comparative test specimens were formed using cementitious mixtures based upon equal parts of alpha calcium 25 sulfate hemihydrate and either Type I portland cement (containing 9.47% tricalcium aluminate) or Type V portland cement, containing 3.82% tricalcium aluminate. The test specimens were immersed in water for a period of one year. As explained in Lehman, the formation of ettringite in the set cement by the reaction of tricalcium aluminate with sulfate caused the specimens based upon the Type I cement to expand and become deteriorated to the point of failure after water immersion for a period of 12 months. For the specimens based upon Type V portland cement, expansion due to ettringite formation was minimized. These specimens showed little or no evidence of failure for periods ranging up to 21 months.